1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and a method for dust prevention of the liquid crystal display apparatus.
2. Description of the Related Art
A liquid crystal display apparatus is widely used as a monitor and the like of office automation equipment and a television because of its superior characteristics of compactness, thinness, light weight and low electric power consumption. The liquid crystal display apparatus includes a liquid crystal panel formed by interposing liquid crystal between two of transparent substrates facing each other, a backlight unit which generates backlight that illuminates the liquid crystal panel, and the like. The liquid crystal display apparatus of a thin type usually uses the backlight unit of an edge light type.
The backlight unit of this type includes a frame-shaped chassis, a frame-shaped shield plate, a light guide plate, a light source, an optical member, a reflecting member and the like. The chassis and the shield plate hold and fix each of constituent members in them. The light guide plate is disposed inside the chassis and guides the light emitted by the light source. The light source is disposed at the edge face of the light guide plate. The optical member is disposed on the front surface (i.e., at the side of the liquid crystal panel) of the light guide plate, diffuses and uniforms the light coming from the light guide plate, irradiating the light on the liquid crystal panel. The reflecting member is disposed on the back face (i.e., opposite side to the liquid crystal panel) of the light guide plate, and reflects the light going from the back face of the light guide plate toward the light guide plate.
One example of the conventional liquid crystal display apparatus is described with reference to FIG. 1 to FIG. 3C. FIG. 1 is a cross-sectional view showing the structure of the main constituent members of one example of the conventional liquid crystal display apparatus. FIG. 2 is a rear view (plan view viewed from the rear side) of the example of the conventional liquid crystal display apparatus. Here, the cross-sectional views taken along the line I-I in FIG. 2 from the arrow direction is FIG. 1. FIGS. 3A, 3B and 3C are perspective views schematically showing the assembling procedure of the example of the conventional liquid crystal display apparatus.
As shown in FIG. 1 and FIG. 3A to FIG. 3C, the conventional liquid crystal display apparatus mainly consists of a backlight unit 10 and a liquid crystal panel 1. The conventional liquid crystal display apparatus further has a frame-shaped front side shield plate 2. As shown in FIG. 1, the front side shield plate 2 has a sectional shape which covers the peripheral portion (outside perimeter) of the display surface of the liquid crystal panel 1, and the side surface of the backlight 10. As the assembling procedure of such a liquid crystal display apparatus, starting from the state shown in FIG. 3A, the backlight unit 10 is assembled to the back surface of the liquid crystal panel 1 to be in the state shown in FIG. 3B. Then, the front side shield plate 2 is assembled to this to complete the liquid crystal display apparatus (FIG. 3C).
As shown in FIG. 1, the backlight unit 10 is provided with a frame-shaped chassis 3, a light guide plate (not shown) held by the chassis 3 and a back side shield plate 6 which covers the side surface of the chassis 3 and the back surface of the light guide plate. The light guide plate is not shown in FIG. 1, and is disposed in a space shown by the reference numeral 9. In the case of an edge light type backlight unit, the light source is disposed at one edge surface of the light guide plate, and the light from the light source is guided to the back surface of the liquid crystal panel 1 by the light guide plate. In the case of a direct light type backlight unit, the light source is disposed directly under the light guide plate. In the chassis 3, a spacer 5 is interposed on the face on which the liquid crystal panel 1 is mounted. A circuit board 7 for driving the liquid crystal panel 1 is mounted to the outer surface of the back side shield plate 6, or the side surface of the chassis 3. The circuit board 7 and the liquid crystal panel 1 are connected with a TCP (Tape Carrier Package) 4 that is a connecting member constituted of a flexible tape. The TCP 4 is an LSI driver that operates the liquid crystal panel 1, and may be a COF (Chip On Film). The circuit board 7 connected with the TCP 4 supplies a signal which drives a semiconductor element such as a TFT integrated on the liquid crystal panel 1.
The dust prevention measures in the conventional liquid crystal display apparatus as described above mainly include the following methods.
(1) Method for preventing entry of dust into the liquid crystal display apparatus by bringing the liquid crystal panel 1 into close adhesion to the backlight unit 10.
However, in this method, in order to enhance close adhesion between the liquid crystal panel 1 and the chassis 3, it is necessary to use a member having a certain degree of stickiness such as silicon, as the spacer 5. In this case, a stress difference occurs due to unevenness in close adhesion to the liquid crystal panel 1 by the influence of heat or the like occurring inside the liquid crystal display apparatus, and the stress difference is likely to cause uneven display.
(2) Method for reducing the clearance until the front side shield plate 2 and the liquid crystal panel 1 are brought into contact with each other. Alternatively, the preventing method for slipping of dust by adding a barrier at the side of the liquid crystal panel surface, of the opening of the front side shield plate 2, and bringing the barrier into contact with the liquid crystal panel 1 to suppress the gap.
However, in this method, there is also the possibility of occurrence of the problem of uneven display. This is because the spot of contact between the surface of the liquid crystal panel 1 and the constituent member such as the front side shield plate 2 contact or closely adhesion to each other is in the state in which stress such as pressure is applied to the surface of the liquid crystal panel 1, and the optical characteristics of the liquid crystal panel 1 partially differ.
Further, another example of the conventional liquid crystal display apparatus is described by using other drawings. Japanese Patent Laid-Open Publication JP 2002-108238A discloses the information terminal equipment including a liquid crystal display. FIG. 4A is a sectional view showing another example of the conventional liquid crystal display disclosed in this JP 2002-108238A. FIG. 4B is an enlarged cross-sectional view of a circular portion A in FIG. 4A.
The information terminal equipment is capable of realizing dust prevention without using a dust preventing cushion, reducing cost and simplifying the assembling process.
As shown in FIG. 4A and FIG. 4B, in the information terminal equipment, the case 11 includes an opening for setting a screen 13, and the screen 13 is disposed in the opening to form the display part. The back surface of the screen 13 is bonded to the case 11 by a double-face coated adhesive tape 14 in the opening. Further, the double-face coated adhesive tape 14 bonds a frame rib 16a of a fixing member (LCD frame) 16 which contains a liquid crystal display 15 to the screen 13. In order to bond the screen to the frame rib 16a, the double-face coated adhesive tape 14 is provided on the area wider inside than the screen sticking surface.
In the above conventional example, the information terminal equipment body is formed by the case 11 including the display part and the cover not shown. In the information terminal equipment body, the liquid crystal display 15 is mounted to the circuit board 12 via the LCD frame 16. The screen 13 is stuck to the outer periphery of the opening for the liquid crystal display part of the case 11 by the double-face coated adhesive tape 14.
The LCD frame 16 has a space for containing the liquid crystal display 15, and includes the frame rib 16a which is fitted inside the opening for the liquid crystal display part of the case 11. The frame rib 16a is formed to have the same height as the screen sticking surface of the case 11 at the time of assembly. The frame rib 16a reaches the back surface of the screen 13 to be stuck, and thereby makes it possible to bond the screen 13 to the double-face coated adhesive tape 14 which bonds the screen 13 to the opening for the liquid crystal display part. Thus, the frame rib 16a fills the role of keeping hermetical sealing with the screen 13.
Accordingly, the LCD frame 16 containing the liquid crystal display 15 closely adheres to the screen 13, whereby, the periphery of the liquid crystal display 15 is sealed, and slipping path of dust or the like can be prevented without adding a dust-proof cushion or the like.
However, in this conventional example, the screen 13 is provided at the front surface of the liquid crystal display 15, and therefore, there arises the problem of unfavorable visibility of the liquid crystal display 15.
As still another conventional example, a liquid crystal display apparatus using a metal casing for prevention of occurrence of dust such as resin dust is disclosed in Japanese Patent Laid-Open Publication JP 2001-330817A. In this example, the liquid crystal panel is disposed in the metal casing, and the liquid crystal panel and the metal casing are bonded to each other by using a double-face coated adhesive tape.
In this conventional example, the spot of contact between the liquid crystal panel and the constituent member and closely adhesion to each other is in the state in which a stress such as pressure is applied to the liquid crystal panel, and the optical characteristics of the liquid crystal panel partially differ. Therefore, there is the problem of occurrence of uneven display.